Growing concern about the global environment issue has led to advances in the conservation of resources and energy. Considerable progress has been made in the development of energy resources that can be used as renewable “clean” energy, and systems thereof. Fuel cell systems in which hydrogen serves as the energy source have a particularly wide range of applications, such as in alternative automobile engine technology, distributed power sources, and cogeneration technology.
The popularization of cellular telephones and other such personal information devices has advanced the development of large-capacity cells to power these devices. One promising technology in this field is fuel cells that make use of hydrogen, methanol, or other such fuel.
FIG. 3 shows the basic structure of a fuel cell. A fuel cell is made up of a fuel electrode for producing electrons and protons by reacting a fuel such as hydrogen, electrolyte for transmitting the produced protons, and an oxygen electrode for reacting electrons supplied through an external circuit with oxygen and protons.
The reactions in the electrodes of a fuel cell have the following roles, respectively.
As to the fuel electrode, a fluid fuel that is a liquid or gas reacts with a catalyst on the electrode, with this reaction comprising H2→2H++2e−, for example. The resulting charge-separated electrons are transferred from the electrode to an external circuit, and protons are transferred to a proton-conductive electrolyte. The electrolyte serves to transmit just protons, and one whose efficiency is decreased only minimally by the diffusion of fuel, etc., is used.
As to the oxygen electrode located across from the fuel electrode, electrons and protons produced in the fuel electrode arrive and react with the oxygen in the air or with oxygen gas in the presence of a catalyst, and water is produced in a reaction comprising O2+4H++4e−→2H2O.
The result of above reactions is that electrical power can be obtained from the energy of hydrogen, methanol, and other such renewable energy sources, and since the reaction product is water, there are no environmental problems.
As discussed above, the necessary components of an electrode used in a fuel cell are a fuel fluid (gas or liquid), a catalyst that serves as the reaction site where the reaction between electrons, protons, and fuel will occur, and an electrode material and an electrolyte for transporting the charge of the electrons or protons. It is thus important to create an environment affording the optimal coexistence of a charge conductor, a catalyst, and a space through which the fuel will flow. Particularly when the electrode is made using a fluoropolymer having sulfonic acid groups on its side chains, which is a proton-conductive solid electrolyte, as the electrolyte, it can be made by molding carbon particles or the like that support a catalyst, and coating the resulting conductive porous material with an electrolyte, or by embedding an electrode in this porous electrode (eg, WO96/508535 or Japanese Unexamined Patent Publication 2000-154273).
One known method for manufacturing a fuel cell comprises a step in which a fuel electrode and an oxygen electrode are produced, a flat electrode material supporting a platinum catalyst is pressed in a direction perpendicular to the plane of the electrode material, and the surfaces of the fuel electrode and the oxygen electrode are then impregnated by being coated with a fullerene derivative-based proton conductor (Japanese Unexamined Patent Publication 2002-110196, and especially paragraph [0031]).